Lennox furnace E200: Hard lockout — rollout circuit open
E200 is a hard lockout because the flame rollout circuit is open, or was open. Lennox's instruction is to correct the cause of the rollout trip, not simply to replace the switch.
Applies to: Lennox gas furnaces with a seven-segment diagnostic display on the control board, such as the ML193UHEK, per installation instructions 508565-01.
What it means
Rollout switches are manual-reset thermal limits mounted at the burner opening, outside the combustion chamber. They trip when flame or hot combustion gas rolls forward out of the burner box instead of being drawn through the heat exchanger and up the flue. Lennox makes this a hard lockout rather than a soft one, meaning the furnace does not clear it on a timer and try again — it stays down until the fault is recovered. That is deliberate. The wording of the code matters too: it covers a circuit that is open now or was open previously, so a rollout that tripped and was reset by hand still leaves the record behind. Lennox's stated action is to correct the cause of the trip, or replace the switch, and then test furnace operation.
Most common causes
- A blocked or restricted flue, vent or intake, so combustion gas cannot leave.
- A cracked or blocked heat exchanger.
- A failed inducer, so flue gas is not being drawn out.
- A burner problem directing flame forward out of the burner box.
- A failed rollout switch that is open with no rollout present, which is the least likely of these.
How to diagnose it
- Do not reset and rerun to get heat. A rollout trip means combustion products went somewhere they should not.
- Note whether there is any soot, scorching or discolouration visible at the front of the burner compartment.
- Confirm there is a working carbon monoxide alarm on every level of the home, including the level the furnace is on.
- Leave the rest to a licensed technician.
How to fix it
- Licensed technician only. This is the code most directly associated with combustion products entering the living space.
- Expect the flue, heat exchanger, inducer and burners to be inspected before any switch is replaced.
- Replacing the rollout switch without finding why it tripped removes the protection and leaves the cause.
Notes
Lennox's communicating alert code 200 reports the same condition on a communicating system. On this list the E prefix and the hard lockout behaviour are the distinguishing features.
Related
- Alert code 200 — Rollout limit switch open
- Which Lennox code list applies — Lennox uses two code systems, and knowing which you are reading matters
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.
What the fix costs
The hard-lockout design shapes the economics: this furnace will not limp along generating hourly retries while you decide, so the decision is simply when the technician comes, and the honest answer is now. Parts-wise the repair guide brackets rollout work with limit switches at $150–350 — the manual's own action line allows for replacing the flame rollout switch — but the sentence in front of that matters more: correct the cause of the rollout trip. Flame leaves a burner box because something blocked its proper path, and the price follows the something: a vent or heat-exchanger passage obstruction cleared, combustion air restored, or, in the finding nobody wants, heat exchanger damage that moves the conversation to the $1,000–2,500+ range where furnace replacement math takes over. The manual's closing step — test furnace operation — is included in any legitimate quote.
DIY or call a pro
The phrase “or previously open” in this code's definition is the homeowner trap: rollout switches are manual-reset devices, so a furnace displaying E200 while seeming fine may have already been reset by someone — and the control is telling you it remembers. Resetting the button (it is a small red button on the switch body) is physically trivial and diagnostically reckless, because the switch is a witness to flame physically escaping the burner compartment; pressing it without knowing why it tripped re-arms the furnace to repeat the event. Leave the furnace locked out, leave the button alone, and treat the call as same-day. History worth reporting: soot marks or scorch discoloration around the burner opening, any recent flue or chimney work, and whether anyone reset the switch before you knew what it was.
The same fault on other brands
The rollout-tripped code translates almost word for word across control families — Goodman's Ed on the newer seven-segment displays, York's 5 red flashes on the JCI boards, and the rest are collected on the rollout switch hub. The design choice worth noticing: nearly every family makes this a lockout that survives power-cycling, because every manufacturer reached the same conclusion about letting a furnace retry after flame has come out of the box.
What this looks like
From the outside, this usually shows up as the furnace heats then trips out on high limit — that walkthrough covers what to check in order, and when it stops being a homeowner job.